Specially formulated slow-release additives that provide for the slow release of additives into a fluid such as oil to meet certain performance requirements of the fluid are generally known. In some, the additives are incorporated into thermoplastic polymers which slowly dissolve into the fluid. In others, the additives are incorporated into polymers which are oil-permeable at elevated temperatures. In still others, the additives are incorporated into particles which are fluid-insoluble but fluid-wettable. In still others, fluid soluble solid polymers are provided, with or without additional additives being incorporated into the polymers.
Although these slow-release additives are capable of introducing additives in the fluid being conditioned, it has been discovered that additive gels can be used more effectively to provide for the slow release of additives into a fluid, such as lubricant additives into oil. In particular, it has been found that fluid-soluble additive gels slowly dissolve to their component additive parts when contacted by the fluid. Examples of such additive gels are disclosed in U.S. Pat. No. 6,483,916, filed Jul. 16, 2002, U.S. patent application Ser. No. 10/603,644, filed Jun. 25, 2003, Ser. No. 10/603,894, filed Jun. 25, 2003 and Ser. No. 10/603,517, filed Jun. 25, 2003, which are incorporated herein by reference.
Garvin et al, U.S. Pat. No. 7,000,655, discloses an additive delivery system which includes a container for the additive gel wherein the container has one or more openings to allow contact of the fluid with the gel to cause one or more additive components in the gel to be released into the fluid and the container is located in a housing with a means of mounting the housing between the filter and the filter mounting surface.
Burrington et al, U.S. Pat. No. 6,843,916, discloses an oil filter comprising a housing, a filter for removing particulate matter from the oil passing through the filter, and oil-soluble lubricant additives inside the housing for slow release into the oil.
Although these additive delivery systems are capable of introducing additives into the fluid being conditioned, attaining a specific release rate of components while maintaining physical gel integrity is a critical feature for a practical controlled release gel system. Improper and/or non-uniform release rates may result in less than optimal performance of the fluid being conditioned and lack of physical gel integrity can result in particles of gel breaking off of the larger gel mass present in the controlled release system. These gel fragments are carried by the fluid and may plug filters and engine orifices, which may negatively impact the overall performance of the fluid-utilizing system or device.
Some applications have unique fluid flow characteristics through the fluid system, filter and any additive delivery system present. These fluid flow characteristics, which include fluid pressure, temperature and flow rate, can interfere with an additive delivery system, resulting in undesired or non-optimal additive release rates and a loss in gel integrity, leading to problems discussed above. Diesel passenger cars in particular tend to have oil system flow characteristics that interfere with existing additive delivery systems.
There is a need for additive delivery systems that allow for the desired contact of the fluid with these additive gels, to cause one or more components of the additives in the gels to be slowly released into the fluid, wherein the desired and/or uniform release rate of components is achieved while maintaining physical gel integrity. There is also a need for additive delivery systems that provides the desired controlled release of one or more additives in systems with various fluid flow characteristics, including those seen in the oil system of diesel passenger cars.